This invention is directed generally to improvements in television receivers, and is more specifically directed to an improved vertical sync separator for such a receiver.
Conventionally, television receivers receive a broadcast signal whose components include horizontal and vertical sync pulses in a train of pulses. Because the horizontal and vertical sync pulses are processed separately, the receiver includes a so-called "vertical sync separator" for separating the vertical sync pulses from the horizontal sync pulses.
To separate the vertical sync pulses from the train of pulses, it is conventional to apply the train of pulses to a second or third order low pass filter. The filter's output ideally consists of a signal representative of only the vertical sync pulses. That signal is peak detected to generate an output pulse for synchronizing the vertical scan of the receiver with the broadcast signal.
The practical problem with the conventional vertical sync separator is that it is not economical to include it in an integrated circuit because such a circuit would necessarily include at least two output pins from the circuit devoted only to the separator function. One pin is needed for access to the low pass filter and another pin is needed for access to a relatively large capacitor associated with the peak detector. Both the low pass filter and the peak detector typically require the use of capacitors whose size makes them impractical for integration. Hence, although much of the receiver's circuitry has been constructed in integrated circuit form, the vertical sync separator is one circuit which has impeded full integration of the receiver's signal processing circuits.
In contemplating the integration of a vertical sync separator, an important feature thereof is satisfactory performance under sub-standard signal conditions. High level impulse or thermal noise in the composite sync signal can cause loss of vertical synchronization in the receiver if the sync separator is overly sensitive to noise. This fact, of course, complicates the integration of the sync separator, but must be accounted for in any practical design.